In recent years, the substantial increases in the energy costs of heating and cooling has encouraged the development of new and better insulation materials and many new insulation materials have been developed in an attempt to satisfy this need.
In recent years, the substantial increases in costs of basic materials such as plastics, cement, asphalt and the like has also encouraged development and use of filler materials to reduce the amount and costs of the basic materials used and the weight of the finished materials. One of the newly suggested filler materials utilizes hollow glass microspheres. The known methods for producing hollow glass microspheres have not been successful in producing microspheres of uniform size or uniform thin walls which makes it very difficult to produce filler and insulation materials of controlled and predictable physical and chemical characteristics and quality.
One of the existing methods of producing hollow glass microspheres for use as insulating materials, for example, as disclosed in the Veatch et al U.S. Pat. No. 2,797,201 or Beck et al U.S. Pat. No. 3,365,315 involves dispersing a liquid and/or solid gas-phase precursor material in the glass material to be blown to form the microspheres. The glass material containing the solid or liquid gas-phase precursor enclosed therein is then heated to convert the solid and/or liquid gas-phase precursor material into a gas and is further heated to expand the gas and produce the hollow glass microsphere containing therein the expanded gas. This process is, understandably, difficult to control and of necessity, i.e. inherently, produces glass microspheres of random size and wall thickness, microspheres with walls that have sections or portions of the walls that are relatively thin, walls that have holes, small trapped bubbles, trapped or dissolved gases, any one or more of which will result in a substantial weakening of the microspheres, and a substantial number or proportion of microspheres which are not suitable for use and must be scrapped or recycled.
In addition, in some applications, the use of low density microspheres presents a serious problem because they are difficult to handle since they are readily elutriated and tend to blow about. In situations of this type, the filamented microspheres of the present invention provide a convenient and safe method of handling the microspheres.
It is also been suggested that hollow glass vacuum microspheres having a reflective metal deposited on the inner wall surface thereof be used to make insulating materials. There have been several methods suggested for making this type of hollow vacuum microsphere but to date none of the known methods are believed to have been successful in making any such microspheres.
Further, the existing methods practiced to produce hollow glass microspheres usually rely on high soda content glass compositions because of their relatively low melting points. Many of these glass compositions were found to have poor long term weathering characteristics.
Thus, the known methods for producing hollow glass microspheres have therefore not been successful in producing microspheres of uniform size or uniform thin walls or in producing hollow glass microspheres of controlled and predictable physical and chemical characteristics, quality and strength.
In addition, applicant found in his initial attempts to use an inert blowing gas to blow a thin molten glass film to form a hollow glass microsphere that the formation of the glass microsphere was extremely sensitive and that unstable films were produced which burst into minute sprays of droplets before a molten glass film could be blown into a microsphere and detached from a blowing nozzle. There was also a tendency for the molten glass fluid to creep up the blowing nozzle under the action of wetting forces. Thus, initial attempts to blow hollow glass microspheres from thin molten glass films were unsuccessful.